From Russia With Love: The First Topological Metal with Termination-Dependent Surface Band Structure and Strong Spin Polarization
Topological metals are materials with nontrivial band crossings or band inversions near the Fermi energy, giving rise to peculiar quasiparticle excitations. Prominent examples include Dirac, Weyl, nodal-line, and nodal-surface metals. In topological metals, bulk superconductivity can also coexist with topologically nontrivial states, enabling the intriguing perspective of Majorana Fermions in solid-state physics.
Among the various families of materials showing gapless Dirac Fermions, the transition-metal dichalcogenide TMX2 (TM = Pd, Pt; X = Se, Te), crystallizing in the same structure as the naturally occurring mineral “moncheite”, was demonstrated to host type-II Dirac fermions, with application capabilities in plasmonics, catalysis, nanoelectronics, and wearable electronics. These properties can be tuned by varying (i) the position of the Fermi level with respect to the degenerate Dirac (or Weyl/nodal line) point and (ii) the strength of the spin–orbit coupling.
Mitrofanovite Pt3Te4 has recently been discovered as a natural mineral in the Kola Peninsula, Russia. Its atomic structure is constituted by alternating layers of hexagonal PtTe2 and Pt2Te2 (or PtTe) which are stacked along the vertical direction and held together by weak van der Waals interactions.
Here, we explored the electronic properties of Pt3Te4 by means of scanning tunneling microscopy (STM)/spectroscopy (STS) and spin- and angle-resolved photoemission spectroscopy (spin-ARPES) in conjugation with density functional theory (DFT). We demonstrate that mitrofanovite is a topological metal hosting spin-polarized surface states. Interestingly, we find that Pt3Te4 has two distinct surface terminations with radically different electronic properties. These distinct terminations are observed at different terraces on the same face of the cleaved crystal. Despite differences in the corresponding electronic band structure, both surface terminations host spin-polarized states, exhibiting typical polarization reversal across the zone center, characteristic of spin-momentum locking. Thus, mitrofanovite offers termination-dependent electronic and surface properties enabling tunable device functionalities for nanoelectronics, spintronics, optoelectronics, and plasmonic applications.